Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fiber

Nawell Ould Moussa,Alessandro Tonello,Vincent Couderc,Marc Fabert,Guy Millot,Tigran Mansuryan,Fabio Mangini,Katarzyna Krupa,Alioune Niang,Mario Ferraro,Charles-Henri Hage,Mario Zitelli,Luca Leggio,Massimiliano Papi,Stefan Wabnitz

doi:10.1038/s41598-021-96753-2

Abstract

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibers. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence (NF) microscopy and endoscopy using multimode optical fibers. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum (SC) generation is well-suited for large-band NF imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

Highlights

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (MMFs) has been recently reported by different research groups
In order to enhance the performance of nonlinear imaging systems up to their limits, the full spatiotemporal dynamics of the self-cleaning process can be exploited. This is the purpose of this Letter: we demonstrate that the spatiotemporal character of BSC leads to a significant resolution enhancement in multispectral-multiband multiphoton fluorescence imaging, in both microscopy and endoscopy configurations
The microscope was composed of a scanning system, a microscope objective (LUMFLN60XW, Olympus), a set of band-pass filters coupled with dichroic mirrors, and two photomultiplier tubes placed before, or after the MMF, in order to measure the emitted fluorescence in microscopy, or endoscopy configurations

Summary

Introduction

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (MMFs) has been recently reported by different research groups. The main serious drawback of these wide-field imaging systems is that any slight fiber movement changes the random mode coupling process This strongly modifies the fiber transmission matrix, which needs to be updated by performing additional measurements. Spatial wavefront shaping permits the pre-compensation of the disorder experienced along the propagation, so that one can optimize both the focusing p oint[22,23] and the pulse d uration[24,25] of the output beam In this way, one can combine both high spatial resolution and efficient nonlinear imaging; an additional scanning of the sample is used to obtain the images. The new systems and approaches of such a multiband sources are still very interesting

Methods

Results

Conclusion